Binding of Fluorescein isothiocyanate labeled recombinant sperm immobilizing factor to mouse sperm. (a) Mouse sperm with FITC dye alone showed no florescence from head and neck region of sperm (b) Fluorescence was observed on whole sperm. Intensity of fluorescence was more in head and neck regions. Magnification: 400X. (c) & (d) Mouse sperm incubated with un-labelled r-SIF and sperm suspended in PBS did not show any fluorescence.